The invention relates to an aluminum/steel transition joint and the method of making the resultant composite metal using an explosive force.
In the past, aluminum and steel have been directly bonded together by explosion techniques to form aluminum/steel joints. U.S. Pat. No. 3,583,062, to Sharp et al. generally discloses explosion bonding techniques for bonding aluminum to steel. Transition joints created with the explosive bonding process are necessary for the welding together of these metals due to the metallurgical incompatibility of aluminum and steel when using fusion welding techniques. Such transition joints are essential in the shipbuilding industry in order to join aluminum structures to steel decks. These directly bonded transition joints between aluminum and steel are, however, subject to bond quality deterioration upon heating to temperatures above approximately 700.degree. F., necessitating critical control of welding parameters during fabrication, frequently at the detriment of fabrication weld quality.
It is well known that interlayer metals between the aluminum and steel can reduce or eliminate the deterioration problem. U.S. Pat. No. 3,630,694 to T. J. Enricht discloses the use of a ferritic stainless steel interlayer to increase the deterioration threshold temperature by approximately 100.degree. F. Titanium interlayers have been shown to increase the deterioration threshold to over 1000.degree. F. The titanium-steel system, however, does not produce a tough bond. Thus, if sufficient stress is concentrated in the titanium/steel bond zone to initiate fracture, brittle catastrophic failure of the transition joint can occur. U.S. Pat. No. 4,612,259 to Ueda discloses the simultaneous use of two interlayers, first tantalum or niobium, and then copper, nickel, or copper-nickel, between titanium and steel to improve bond toughness of bonded and hot rolled clad. Both tantalum and niobium are very expensive and limit the practicality of the disclosed product.
It is therefore the object of the present invention to provide an improved aluminum/steel transition joint comprising interlayers of both titanium and copper-nickel to achieve a durable bond with thermal stability and superior strength.
It is a further object of the instant invention to provide a method for forming an improved aluminum/steel transition joint utilizing explosive force.